Benjamin Zephaniah talks like an Olympic athlete - he takes words and runs with them. At the end of more than two hours with him, I felt about to expire, even though I was only a spectator at the marathon. His rap poetry also seems to move - occasionally to its detriment - faster than thought; his superb novels for teenagers don't dawdle either. His latest, Refugee Boy, is a winner. And he is such a spellbinding performer that I realised he could be saying anything at all and I would be stopped in my tracks.

No wonder, then, that such a narrator should want to be in charge of his own legend. But Zephaniah has this difficulty: legends are created by other people. It is not easy for him to hold on to his version of his life - not least because there is no shortage of people who would like to subsume him, make him part of their story.

I was expecting Zephaniah to tower above me, rather as his writing, at its best, soars. In photographs, the length of his dreadlocks (which, close to, look like unused garden twine) suggested a giant. But he is of average height - slender and graceful, too.

At this point, I ought not to describe his face. For in his brilliant first novel, Face, about a boy who has to undergo plastic surgery, he warns against judging by appearances. He calls it 'facial discrimination'. But it is his face that holds the attention absolutely: it can look seraphic one moment, wicked the next. He is bad boy and holy man rolled into one, with a gap-toothed smile and an ironic gleam in his eyes.

We met in Newham in the East End of London, in the local bookshop, the Newham Parent Centre. It is run by Vivian Archer, who dotes on Zephaniah, and would appear to be his second home. He wanted me to know everything about it: the help it gives to the community, to parents, children and refugees. He told me he had met the Ethiopian refugees who inspired him to write Refugee Boy just round the corner. But before anything else, he wanted me to know that even the two cats in the bookshop are 'supported by the local community, who club together to pay for vet's bills'.

He has always been a man of causes little and large. He is ferociously critical about Britain but passionately attached to it, too. 'I gotta say I love this country, though I rail against it all the time. We all wanted a one-way ticket to Africa, but when I got there, I couldn't wait to get back.' He likes Britain partly because it is possible to criticise it.

His eloquence and sense of humour make Zephaniah attractive to those in need of a spokesman. Was there any danger, I wondered, of his becoming the equivalent of a glorious brooch for the white establishment to pin on its lapel? The thought has not escaped him.

The Labour Party invited him on a consultative committee for arts in the national curriculum but he resigned when he felt his words were being made to toe a party line. Earlier this year, the Metropolitan Police wanted to use a couple of lines of his poetry ('I love this concrete jungle still with all its sirens and its speed/ the people here united will create a kind of London breed') for a recruitment campaign. Zephaniah would not play. He complained that he was still stopped by the police, simply because of his appearance. Now he is less vociferous: 'I would love to see a day when I am able to work for the police. I'd be happy, because they pay well, I'm told.' He is never short of a joke. But he won't 'unite' with anyone unless his heart is in it.

Zephaniah was also poet in residence at the chambers of Michael Mansfield QC. He sat in on the inquiry into Bloody Sunday and on the case of Ricky Reel, the Asian student found drowned in the Thames. This collaboration was more positive and led to his latest collection of poetry, Too Black, Too Strong (Bloodaxe), in which he uses legal language as a satirical weapon. The best poem in the collection is 'Appeal Dismissed', about a Polish refugee sent home because rape was not considered by the judge to be torture. 'I don't really feel I wrote it. The judge wrote it for me. In a way, I feel sorry for the judge.'

Zephaniah has an extraordinary ear for poetry and, as the new practitioner of an ancient oral tradition, he has attracted the attention of Oxford and Cambridge Universities and lectured at both. Cambridge wanted to make him a fellow of Trinity College and he was considered for professor of poetry at Oxford. He was even tipped for poet laureate (though Andrew Motion got the job).

But his fan club is by no means all white. Nelson Mandela read and admired Zephaniah's poetry in prison; Bob Marley liked it, too. Zephaniah has returned the compliment, adapting one of Marley's songs in his poem 'I Neva Shot De Sheriff'. He has performed with the Wailers, too, after Marley's death. He told me he once met Marley in Earl's Court and was bowled over by him. 'He was a spiritual intellectual,' he concluded. Clearly, he aspires to something similar himself.

The Zephaniah legend (as I see it) is of a Rastafarian prodigal son, born in 1958 in Handsworth, son of a Barbados postman. He was dyslexic, attended an approved school but left at 13 unable to read or write. He got into trouble with the law, even spent some time in jail for burglary. But when I asked what crimes he committed, he hesitated, uncharacteristically: 'Everything. I was growing up nicking things from cars and people's houses, fighting with the police... but don't make too much of it. It is such a long time ago - and not how I want to be defined.' He learned more, he wanted me to understand (or 'overstand' - one of his favourite coinages) from 'seeing my mother suffer' when his father beat her up.

He has tended to seem, if anything, more nervous about being associated with poets than with criminals. Even in a light poem for children, his wish not to be branded is evident: 'I used to think nurses/ Were women,/ I used to think police/ Were men/ I used to think poets/ Were boring,/ Until I became one of them.'

When I met him, however, a new story emerged. He used to say that he composed his first poem in his twenties. Now he admits that his whole childhood was 'doing poems'. And although his mother is no poet, he said: 'Caribbean women are always doing poems... I remember my mother passing recipes on to my sister in rhyme.'

Then he told me that when he was only eight he got a friend to 'send in one of my poems to the BBC'. He invented a pseudonym, 'Wilfred Watson', and claimed to come from Kidderminster, which sounded posher than Handsworth.

Could he still remember the poem? He leant forward, fixed me with a look and began: 'Wonder wonder why I live,/ My heart and soul to life I give/ Upon the wetted grass I lie/ If death should call me/ If I should die/ In vain I strive for need and require/ No smoke can dark my burning fire.'

'It's mumbo-jumbo,' he laughed, but listening to it, I didn't think it was, entirely.

Nor did the BBC, which had its own view on the sort of man that had produced the poem. Zephaniah chuckled at the memory and impersonated the broadcaster who had speculated about Mr Wilfred Watson's character: 'Here is a man who is tired of life, a mature man...'

Zephaniah is a mature man now and anything but tired of life. Yet he has one overwhelming regret: he is unable to have children. For more than 10 years, he was married to Amina, a theatrical administrator. He is divorced now, although he says he 'hates the word'.

The greatest love of Zephaniah's life, it turns out, has always been his mother. You can find her in the anthology of love poetry that he edited for Bloomsbury, in a poem that begins: 'I luv me mudder an me mudder luvs me/ we cum so far from over de sea.' We're given a few tantalising details about her: she has big muscles, likes cashew nuts and cats. Her name is Valerie. But he has never given away much about her, let alone explained why she is so vital to him. Could he bring his 'mudder' into the room for me? I loved the way he answered this question, as if embarking on a novel:

'A boat called the Empire Windrush brought all the men over from Jamaica. The next boat was full of women in 1954, including my mother. She had seen the posters that read: "Britain, the mother country wants YOU".' When she arrived, she marvelled at the number of English people that seemed to 'live in factories' (because all the houses had chimneys).

'She is a strong Christian but realises that her children [all nine of them] are different.' Zephaniah is the eldest and has a twin sister, for instance, who is a 'hard-line fundamentalist Jehovah's Witness'.

His relationship with his mother, like many a love story, includes elopement: 'We ran away together [in flight from his father]. We had to knock on doors together; we were homeless. Sometimes, we'd be offered a room with a single bed and, as a teenage boy, I'd then have to share it with my mother.' She is 'large', he added, as if squashed by the memory. 'Whenever I am in Birmingham, I have to come and eat her dumplings. And I speak to her on the phone, every day, without fail.' She is delighted by his triumphs but: 'She keeps asking me, "Will you stop saying those bad things about the Government?"' Her proudest moment was when Ealing Hospital named a ward after him. As an ex-nurse herself, it was this that 'touched her most'.

Zephaniah does not know whether having his own children would have held him back, stopped him from being a black Pied Piper. I told him I see him as an honorary father to an extended family too populous to count. He often talks to kids in schools. 'When they ask me what the fuck is education for?, I can tell them, cos I ain't got it.' He added: 'I tell kids all the time the education system measures intelligence in only one particular way.'

Once, he was working 'with young black kids in trouble with the police'. He slumped in his chair to show how unimpressed his audience was with him. What made them sit up was the moment when he was introduced as 'Doctor Benjamin Zephaniah'. 'Have you got "Doctor" on your driving licence?' they wanted to know. And: 'Have you ever been stopped by the police? And: 'Could you ask the police to call you doctor?' Zephaniah replied: 'Yes, yes and yes.' The kids went wild: 'Rasta doctor! That's bad, man.'

He finds it easier to talk to young people than to adults because their minds are 'much more open'. Children are quick to pick up, he explained, the irony of being told incessantly not to fight while those in power promote extravagant wars.

Had he written about the bombing of Afghanistan? Or was the war too formless? 'And shapeless,' he replied. He then volunteered: 'When it happened, I was so surprised that so many people were so surprised. America is the bully of the planet and I know the laws of the playground. If you bully people, they are going to come back to you.'

He thinks the West is playing into the Taliban's hands. 'All the things the Taliban have told them about the West, they're now doing.' Slowing down, he said he had a message for Bush: 'I say to him: if you keep giving an eye for an eye, you end up in a world of blind people.' The light went out of his voice as he spoke. It was quite a moment.

He would like to take me to the coffee house down the road, he said, next to the mosque, where Afghans, 'mainly older men', meet. They are 'really angry', he said. But he impressed me by adding that he doesn't write about the war now because he 'might be wrong' in his views. The thing is 'too massive' to be sure of anything.

In spite of Zephaniah's success, there remains an insecurity about him. He needs his fans, and, I think, to tell me about them. Yet it was impossible not to feel moved by what he had to say. When I asked him what his proudest moment had been, it was an even contest between meeting Mandela and receiving a letter from an unknown Asian woman. The woman, in her late thirties, had suffered 'facial disfigurement after her husband had poured boiling oil on her for daring to look at another man'. Since then she had not left her house. But she wrote: 'After reading your book [Face], I'm going out shopping. I'm going to buy myself a new dress.'

Letters like these put Zephaniah beyond criticism. No quibbles apply. Overstanding is everything.

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